NEW YORK ( TheStreet) -- Here are this week's winners and losers.

Winners

iPath Dow Jones UBS Grains Subindex Total Return ETN ( JJG) 8.0%

Many components of the commodities spectrum continued to behave in a volatile fashion over the past week. However, ETNs designed to track the performance of agricultural products were a source of strength.

Upward action from corn and other grains helped JJG power back through its 50-day moving average. Currently the fund is hovering around levels witnessed before its late April selloff.

iShares MSCI South Africa Index Fund ( EZA) 2.2%

South Africa proved to be an attractive region of the globe last week, leading EZA to a nice bounce off its 200-day moving average. Despite this week's strength, investors should continue to use caution when taking steps into this emerging-market fund.

EZA is designed to track the largest and most liquid companies in the nation and is heavily weighted towards the materials sector. Given the shaky action in commodities recently, this sector may prove volatile in the days ahead.

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Market Vectors Coal ETF ( KOL) 2.5%

The coal industry got a lift throughout the past week, sending KOL to industry-leading gains. Joy Global ( JOYG) made headlines at the week's onset, when it announced the purchase of LeTourneau Technologies from Rowan ( RDC).

May has been tough for this fund. Since the start of the year, shares have stuck to a steep downward path. In the event of continued weakness from KOL down the road, investors may want to keep a close watch on the $45 level. Between the end of January and the middle of March, the fund bounced against this point five times.

Losers

Market Vectors Vietnam ETF ( VNM) -10.3%

The inherent volatility of frontier markets shone through last week as VNM fell steadily on every trading day. By Friday's close the fund was trading at all-time lows.

This week of downward action can be traced back to the nation's central bank, when the State Bank of Vietnam boosted interest rates early in the week in an attempt to control inflation. According to a report from Bloomberg, this marks the sixth increase in 2011.

Looking ahead, inflation will likely continue to be a major factor to keep an eye on when weighing international ETF options.

iPath S&P 500 VIX Short Term Futures ETN ( VXX) -3.2%

Although political and economic turmoil continues to rage across many regions of the globe, investors still appear to be confident in the ongoing economic recovery. As a result, the fear-based VIX and the ETFs designed to track it, headed south.

With the past week's decline, VXX has retreated to brand new record lows. The iPath S&P 500 VIX MidTerm Futures ETN ( VXZ), meanwhile, continues to hover around previous all- time lows.

Guggenheim Solar ETF ( TAN) -6.4%

It has been a cloudy couple of weeks for the solar energy ETFs. Since the start of May, TAN has stuck to a steady downward path. Friday was a particularly rough day for TAN and Market Vectors Solar Energy ETF ( KWT). A poor earnings report from top 10 holding, Yingli Green Energy ( YGE), sent shares of the company spiraling nearly 10%.

TAN is currently trading at March lows, while KWT has retreated back to levels seen at the start of the year. As we head into the new week, it will be interesting to see whether they can hold onto these levels.

--Written by Don Dion in Williamstown, Mass.

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At the time of publication, Dion Money Management owned the iShares MSCI South Africa Index Fund and Market Vectors Coal ETF.

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